1. Technical Field
The present invention relates to a vibratory gyroscope and a vibrator capable of being preferably used in this vibratory gyroscope.
2. Related Arts
Japanese laid-open publication Tokkaihei No.7-83671 has disclosed a vibratory gyroscope using a tuning-fork vibrator made by joining a total of three vibration pieces composed of a middle driving vibration piece and two detecting vibration pieces before being at both sides of the middle driving vibration piece all joined to a base part in one body. FIG. 1 shows the composition of an example of such a vibratory gyroscope. In the example shown in FIG. 1, a tuning-fork vibrator 71 forming a vibratory gyroscope is composed of three vibration pieces which are composed of a middle driving vibration piece 73 and two detecting vibration pieces 72 and 74 arranged at both sides of it nearly in parallel with it, and a base part 75 with which the driving vibration piece 73 and the detecting vibration pieces 72 and 74 are joined in one body.
In the above-mentioned tuning-fork vibrator 71, the driving vibration piece 73 is vibrated in the X-Z plane by a driving means (not shown) provided on the driving vibration piece 73. And the left and right detecting vibration pieces 72 and 74 are resonated in the same X-Z plane. When a turning angular rate xcfx89 acts around the axis of symmetry Z of the tuning-fork vibrator 71, a Coriolis force (f) acts on each of the detecting vibration pieces 72 and 74. Since the detecting vibration pieces 72 and 74 are vibrating in the X-Z plane, vibration in the Y-Z plane is induced in the detecting vibration pieces 72 and 74. A turning angular rate is measured by detecting this vibration by means of an detecting means (not shown) provided on each of the detecting vibration pieces 72 and 74.
In a former vibratory gyroscope of the above mentioned composition, in case of forming the vibratory gyroscope by supporting the tuning-fork vibrator 71, the vibrator 71 is supported by fixing the entire end part 76 of the base part 75 of the tuning-fork vibrator 71 opposite to the other end part at which the driving vibration piece 73 and the detecting vibration pieces 72 and 74 exist, or by fixing an unillustrated supporting vibration piece at a position of this end part 76 corresponding to the axis of symmetry Z. Therefore, it cannot be said that a Coriolis force generated by a turning angular rate is efficiently utilized for action of a detecting vibration in the detecting vibration pieces 72 and 74, and there is a problem that the sharpness of resonance (Q value) of the detecting vibration in the Y-Z plane in the detecting vibration pieces 72 and 74 is low and the measurement sensitivity for a turning angular rate is low.
Recently, a vibratory gyroscope is used as a turning rate sensor in a vehicle control method of an automobile body turning rate feedback system. Such a system detects the direction of a steering wheel itself by a turning angle of the steering wheel. At the same time as this, the system detects a turning rate of the actually turning car body by means of a vibratory gyroscope. The system finds a difference between the direction of the steering wheel and the actual body turning rate by comparing them with each other, and attains a stable body control by compensating a wheel torque and a steering angle on the basis of this difference.
It is necessary to contain such a vibrator into a particular container package, which is then fixed on a fixing member such as a fixing plate. The fixing member is then fixed on a car body. In such a case, the vibrator is adhered onto the fixing plate to fix it thereon.
However, in a car body control system, a vibratory gyroscope and its vibrator is subjected to a wide range of environmental temperature, including high and low temperatures. Such temperature range is normally xe2x88x9240xc2x0 C. to +80xc2x0 C., and may be broader when more strict specification is applied. Particularly when applying a vibrator made of a piezoelectric single crystal, the temperature characteristics of the crystal also affects the performance of the gyroscope.
The inventors have tried to eliminate or reduce the temperature characteristics of the vibrator itself. However, when adhering such a vibrator onto a fixing plate and measuring a sharpness of resonance (Q value) of its driving vibration between xe2x88x9240xc2x0 C. it +80xc2x0 C., it was found that the Q value is substantially changed or deviated between xe2x88x9240xc2x0 C. to +80xc2x0 C. For example, if the Q value is substantially constant near room temperature, the Q value is largely changed when the environment temperature of the vibrator is changed towards xe2x88x9240xc2x0 C. or +80xc2x0 C.
An object of the present invention is to provide a vibratory gyroscope which can improve the sharpness of resonance (Q value) of a detecting vibration in a detecting vibration piece and can measure a turning angular rate with a sensitivity.
Another object of the invention is to provide an analyzing method for manufacturing a vibrator having a high sharpness of resonance of a detecting vibration in a detecting vibration piece, and a supporting method and a manufacturing method using this analyzing method.
Another object of the invention is, when adhering a vibrator onto a supporting member, to reduce the deviation of Q value of the driving vibration excited in the vibrator when the environmental temperature of a gyroscope is changed so that the temperature-dependent change of the performance of the gyroscope may be reduced.
A vibratory gyroscope of the present invention is a vibratory gyroscope for detecting a turning angular rate of rotation applied to a vibrator, which vibratory gyroscope a vibrator provided with a plurality of vibration pieces and a base part having the plurality of vibration pieces connected with it and is composed so as to obtain the turning angular rate on the basis of a detecting vibration excited in the vibrator according to the turning angular rate when giving a driving vibration to at least one of the vibration pieces, and supports the vibrator in a domain where the detecting vibration is smallest in the vibrator, said domain being in the vicinity of the center of gravity of the vibrator.
Preferably the vibrator is provided with a supporting hole in a domain where the detecting vibration is smallest in a state where the supporting hole is not provided in the vibrator and the vibrator is supported with or in the vicinity, preferably on or near the inner wall face of this supporting hole.
Supporting the vibrator in the vicinity of the supporting hole means supporting the surface of the vibrator within a range of 1 mm from the periphery of the supporting hole.
Another embodiment the present invention is a vibratory gyroscope for detecting a turning angular rate of rotation applied to a vibrator and the vibrator is provided with a plurality of vibration pieces and a base part having the plurality of vibrating pieces connected with it and the base part is provided with a supporting hole the gyroscope is composed so as to obtain the turning angular rate on the basis of a detecting vibration excited in the vibrator according to the turning angular rate when giving a driving vibration to at least one of the vibration pieces and the gyroscope is provided with a supporting means for supporting the vibrator with or in the vicinity of the supporting hole.
And the present invention is a vibrator formed out of a piezo-electric single crystal and comprises a plurality of vibration pieces each of which performs a bending-vibration and a base part having the plurality of vibration pieces connected with it and said base part is provided with a supporting hole for supporting said vibrator .
Another embodiment of the present invention is a vibratory gyroscope for detecting a turning angular rate of rotation applied to a vibrator, wherein the vibrator is provided with a plurality of vibration pieces and a base part having the plurality of vibration pieces connected with it and is composed so as to obtain the turning angular rate on the basis of a detecting vibration excited in the vibrator according to the turning angular rate when giving a driving vibration to at least one of the vibration pieces, and the vibrator is supported in a domain where the detecting vibration is smallest in the vibrator, said domain being in the vicinity of the center of gravity of the vibrator (when it is not vibrated). As a result it is possible to improve the sharpness of resonance (Q value) of a detecting vibration in a detecting vibration piece, raise the sensitivity, and reduce the influence which the strain of a vibrator, caused by vibration or acceleration given from the outside of the vibrator, exerts on its vibrating state.
Another aspect of the invention is to provide a vibratory gyroscope for detecting a turning angular rate of rotation applied to a vibrator in a predetermined temperature range, wherein the vibratory gyroscope comprises a vibrator, a supporting member for supporting said vibrator and an adhesive portion made of an adhesive provided between said supporting member and said vibrator for bonding said vibrator to said supporting member. The vibratory gyroscope detects a turning angular rate based on a detecting vibration excited in the vibrator according to said rotation when a driving vibration is excited in said vibrator. The adhesive has a tan xcex4 not higher than 0.1 within said predetermined temperature range.
The inventors have searched for the reason why the Q value of the driving vibration excited in a vibrator is substantially deviated dependent on the temperature change. They finally found that it is possible to improve, and to reduce the deviation of, the Q value in the whole temperature range defined in a specification, by reducing tan xcex4 of the adhesive to a value not higher than 0.1.
Tan xcex4 of the adhesive may be preferably be not higher than 0.03 for improving, and reducing the deviation of, Q value in the whole temperature range specified in a specification (normally xe2x88x9240xc2x0 C. to +80xc2x0 C. and more preferably be xe2x88x9240xc2x0 C. to +85xc2x0 C.). The lower limit of tan xcex4 may be 0.00.
The difference between the maximum and minimum values of tan xcex4 of the adhesive in the temperature range may preferably be not higher than 0.03.
The specific gravity of the adhesive may preferably be not higher than 1.1 for further reducing the deviation of the Q value in the temperature range. It is preferable to improve the content of a filler in the adhesive to not more than 7 weight percent for reducing the specific gravity to a value not higher than 1.1 and towards 1.0.
The adhesive includes, but is not limited to, one or more adhesives selected from the group consisting of a synthetic rubber such as silicone rubber (such as silicone RTV rubber), silicone gel, silicone resin, ethylene-propylene rubber, butyl rubber and urethane rubber, a fluoride resin such as xe2x80x9cTeflonxe2x80x9d and ethylene tetrafluoride resin, vinyl chloride resin, xe2x80x9cNylonxe2x80x9d and polyethylene.
The adhesive preferably has a dynamic modulus of elasticity of 102 to 1010 Pa and a dynamic loss of 101 to 108 Pa. The thickness of the adhesive portion may be generally adjusted so as to be inversely proportional to the dynamic viscoelasticity.
The adhesive may preferably be a viscoelastic material with small deviation in its dynamic modulus of elasticity in a temperature range specified in a specification for a vibratory gyroscope. The maximum value of the dynamic modulus of elasticity within the temperature range may preferably be not more than 3 fold of its minimum value in the same temperature range.
The adhesive portion may be formed by any process. For example, liquid material before curing may be applied onto a desired region by means of coating, potting or spray coating to form the end coating layer. For example, silicone adhesives of various types, such as alcohol-liberating, acetone- liberating, oxime- liberating, acetic acid-liberating and addition reaction types, may be potted and adhered onto a desired region by means of a dispenser. When liquid type material is coated or potted on a desired region, such liquid type material may preferably have a viscosity of not more than 100 Paxc2x7s to readily cover a larger area and to produce a coated film with a uniform thickness. A sheet or plate shaped material made of a polymer may be adhered onto a desired region to provide the adhesive portion.
The process for curing an adhesive includes, but is not limited to, curing processes caused by addition reaction of two types of solutions (two-part adhesive), addition reaction caused by heating, and alcohol liberating reaction.
The thickness of an adhesive portion between a supporting portion and vibrator may preferably be not lower than 0.05 mm and more preferably not lower than 0.1 mm for fixing the vibrator with improved reliability. The thickness of an adhesive portion between a supporting portion and vibrator may preferably be not higher than 1 mm and more preferably not higher than 0.4 mm for further reducing the deviation of the Q value within the temperature range and for improving the sensitivity of the detecting vibration.
And as a preferred embodiment, to support a vibrator at a domain where a detecting vibration is smallest and a domain where a driving vibration is smallest overlap each other can raise the Q value of the driving vibration as well as the detecting vibration and further improve the sensitivity.
In a particularly preferred embodiment the end driving vibration and a detecting vibration occur in the plane of a vibrator.
Since the amplitude of a driving vibration is considerably larger than the amplitude of a detecting vibration, it is important to reduce the influence of the driving vibration on the detecting vibration. In a preferred embodiment, a vibrator is supported at or in the vicinity of the center of gravity of the vibrator. Thanks to this, it is possible to minimize the influence of the driving vibration on the detecting vibration.
That a vibrator is supported at or in the vicinity of the center of gravity GO of the vibrator or the center of gravity GD of the driving vibration means that a vibrator supporting point may be located substantially at the center of gravity GO or GD and is within a circle of 1 mm in diameter, said circle having the center of gravity GO or GD as its center.
In a preferred embodiment, a supporting means is joined onto the surface of a vibrator in a domain where the detecting vibration is smallest by adhesion, gluing, soldering, metalizing or the like, or by pressure-joining.
And it is preferable to provide a supporting hole in a vibrator to support the vibrator on the inner wall face of this supporting hole. In this case, it is possible to provide a projection on a supporting means, insert this projection into the supporting hole, put an adhesive agent, a gluing agent, solder or a metalizing paste between the inner wall face of the supporting hole and the projection, and thereby join the vibrator and the projection with each other.
Depending on the shape and size of a vibrator, a domain where a detecting vibration is smallest in the vibrator sometimes does not appear on the surface of the vibrator or appears with a very small area. Accordingly, by providing a supporting hole in a vibrator and supporting the vibrator with this supporting hole, when exposing said domain to the inner wall face of the supporting hole, it is easy to more surely hold the domain where a detecting vibration is smallest.
A supporting hole may be what is called a blind hole but it is most preferably a through hole, and in case that it is a blind hole, the blind hole has preferably a depth of xc2xd or more in comparison with thickness of the vibrator. The reason is that a domain where a detecting vibration is smallest is wider inside the vibrator than on the surface of the vibrator.
In case of providing a supporting hole in a vibrator and supporting the vibrator with or in the vicinity of this supporting hole, in a preferred embodiment, at least part of the supporting hole exists within a domain where a detecting vibration is smallest in the vibrator in a state where said supporting hole is not provided in the vibrator. The reason that this is preferable is described. It has been found that in case that a domain where a detecting vibration is smallest is exposed onto the surface of the vibrator, when this domain is supported, the following problem occurs. That is to say, when a certain time elapses or the ambient temperature changes after a vibratory gyroscope has been assembled, the measurement of a turning angular rate sometimes was not stable.
The inventors have examined the reason and reached the following discovery. That is to say, for example, in a vibrator as described later, when assembling a vibratory gyroscope and then exciting a specified driving vibration in a vibrator and measuring distribution of the amplitude of vibration in each point of the vibrator, the vibration amplitude changes greatly around a node of the vibration. Due to this, it is difficult to coincide a node of the driving vibration and a node of the detecting vibration with each other. Furthermore, even if a domain where the detecting vibration is smallest is accurately supported at a point of time when a specific supporting means, for example, a projection for supporting has been joined with the domain where the detecting vibration is smallest on the surface of the vibrator, the domain where the detecting vibration is smallest may be sometimes moved slightly from its original position due to a change with the passage of time such as a temperature change and the like. Thus, the degree of disturbance caused by contact of a supporting means with the vibrator, said disturbance acting on a vibrating state of the vibrator, changes and the characteristics of the gyroscope changes.
On the other hand, it has been found that the magnitude of a detecting vibration is averaged in a fairly wide range, including a supporting hole and its peripheral area, by providing the supporting hole in a domain where the detecting vibration is smallest in a state where no supporting hole is provided in the vibrator and supporting the vibrator with this supporting hole. Thus, even if a certain time passes or an ambient temperature changes after the vibrator has been first supported with or in the vicinity of the supporting hole, the degree of disturbance exerted by the supporting means upon the detecting vibration has come to be hard to change, movement of the zero point caused by a temperature change has become small and the characteristics of the gyroscope have been greatly stabilized.
Additionally, a higher effect can be obtained by filling the supporting hole with such an adhesive as resin and holding the vibrator through the resin by means of the supporting means.
And in a preferred embodiment, a plurality of supporting holes are provided in a base part and a vibrator is supported by the plurality of supporting holes. By this, when an external vibration is applied to the vibrator, the influence of disturbance caused by this external vibration can be remarkably reduced. In this embodiment, it is preferable to support the vibrator with or in the vicinity of a plurality of supporting holes which are at positions being centrosymmetric with respect to the center of gravity of the vibrator. Thanks to this, the influence of disturbances caused by external vibrations is reduced further.
And it is possible to provide a plurality of supporting holes so as to surround a domain where a detecting vibration is smallest in a vibrator. In this case, it is particularly preferable to support the vibrator with a plurality of supporting holes which are at position being centrosymmetric with respect to the center of gravity of the vibrator.
And in a preferable vibrator, a plurality of vibration pieces comprise driving vibration pieces and detecting vibration pieces, and a supporting hole is provided between one of the detecting vibration pieces and a domain where a detecting vibration is smallest.
And in the above vibrator, it is particularly preferable that the domain where the detecting vibration is smallest in the vibrator extends to the inner wall face of the supporting hole. In this case, preferably, the supporting hole is provided around the domain where the detecting vibration is smallest, and more preferably, it is provided between the domain where the detecting vibration is smallest and a detecting vibration piece.
In a vibratory gyroscope of the present invention, as a material for a vibrator, it is preferable to use piezoceramic or a piezoelectric single crystal such as a single crystal of quartz, a single crystal of LiTaO3, LiNbO3 or the like, and particularly it is more preferable to use a piezoelectric single crystal such as a single crystal of quartz, LiTaO3, or LiNbO3. The reason is that a high Q value of a single crystal itself can be effectively utilized.
A domain where a detecting vibration or a driving vibration is smallest in the present invention indicates one or plural domains where the detecting vibration or driving vibration is smaller than that cannot be found. The vibration amplitude in a detecting vibration or driving vibration is preferably 2/1000 or less of the maximum vibration amplitude point in a vibrator and particularly preferably 1/1000 or less. Preferably, a domain where a detecting vibration is smallest and a domain where a driving vibration is smallest exist locally in part of the base part.
And the present invention computes the ratio of the amplitude of a detecting vibration in a vibrator to the maximum amplitude of the detecting vibration in the vibrator by means of a natural mode analysis by a finite element method and detects a domain where the detecting vibration is smallest from distribution of said ratios in each point of the vibrator. Particularly preferably, it computes the ratio of the amplitude of a driving vibration in each point to the maximum amplitude of the driving vibration in the vibrator by means of a natural mode analysis by a finite element method and detects a domain where the driving vibration is smallest from the distribution of the ratios in the vibrator.